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The size distribution and composition of inclusions in Mg-RE-Ti treated steels with different Al contents were investigated systematically, while the microstructure and the nucleation potency of inclusions for AF were analyzed. The results show that the inclusions were refined with Mg treatment, and then coarsen following La addition in the samples. The particles in high Al sample were more likely to collide, aggregate and form clusters due to the relatively high amount of inclusions in melt steel. The dominate inclusions were composed of two layer structures with Mg-bearing inclusions cores and La-bearing inclusions shells. With the increase of Al content, the cores evolved from MgO to MgO•Al2O3 and the shells evolved from La2O2S and La2O3 to LaAlO3. The nucleation potency of inclusions for AF decreased due to relatively high lattice misfit between inclusions and α-Fe in high Al sample. The AF fraction decreased with the increase of Al content because of the decrease of the amount of effective inclusions. [ABSTRACT FROM AUTHOR]

The size distribution and compositions of inclusions and microstructures in steels with different Mg contents are systematically investigated. The results show that Mg treatment modified and refined the inclusions. With Mg addition, the dominant inclusions in the samples evolve from LaAlO3 with MnS to a Mg‐enriched core enwrapped by a La‐enriched shell with MnS. While the Mg content increases from 11 to 66 ppm, the core changes from MgO·Al2O3 to MgO, and the shell develops from LaAlO3 to La2O2S. With the increase in Mg content from 0 to 44 ppm, the number density of effective inclusions is improved, and the proportion of acicular ferrite (AF) increases from 15% to 39%. However, the AF fraction decreases to 16% due to the relatively low amount of effective inclusions in the sample Mg3 with 66 ppm Mg. [ABSTRACT FROM AUTHOR]

Ce has been widely used in oxide metallurgy for modifying inclusions and refining microstructure. Effect of Ce contents on the evolution and characteristics of non-metallic inclusions and the formation of acicular ferrite (AF) in Ce-treated Ti-Mg-killed EH36 steel was investigated. The results showed that the main type of inclusions in Ti-Mg deoxidized steel was MgO·Al2O3-MnS. After 0.014%, 0.024% and 0.037% Ce were added into the steels, dominant inclusions became CeAlO3-MgO-MnS, Ce2O2S-MgO-MnS and Ce2O2S-MnS, respectively. The precipitation of pure MnS was suppressed in the steel with 0.024% Ce, while the number density of total inclusions increased significantly in the steel with 0.037% Ce, causing the inclusions distributing densely. Ce addition refined the microstructure of tested steels by promoting AF formation and polygonal ferrite distributing evenly. Dispersive distribution, low lattice mismatch against α-Fe, as well as lower number density of pure MnS caused the highest number density of effective inclusions (nucleus of AF formation) in 0.024% Ce-treated steel. [ABSTRACT FROM AUTHOR]